When using previously known methods of cleaning filters or basins of this type, the filter or basin in question must be removed from service and drained of water. A machine, such as a compact loader, is then used to remove the top layer of sand and transport it to a suitable location for cleaning. When the filter is refilled with water following cleaning of the bed, the filtered water must be discharged to waste for two to three weeks before the filter can be returned to normal service, since drying of the sand surface causes disturbance to the microbacterial activity in the bed. Every cleaning operation of this type takes approximately one month and requires the services of three plant workers and an outside contractor. Since two bed cleaning operations are normally carried out annually, involving the removal of a total of about 6 centimeters of sand, the filter must be refilled with sand every ten years.